Ovalbumin-urea interaction study at distinct pH ranges via ultrasonic investigation and molecular dynamics...

This study discusses ovalbumin (OVA)-urea interactions in distinct pH ranges by molecular interaction studies. This interaction is studied experimentally by means of density, ultrasonic velocity, viscosity, and surface tension measurements, along with the analysis of some thermo-acoustical parameters, for OVA (5 mg mL^-1) dissolved in phosphate buffer (pH 2, 5, 7, 9, and 12). The obtained results suggest that the presence of urea weakens water-water interactions and reduces the strength of the hydrophobic effect. In addition, OVA denaturation is found to be somewhat higher in alkaline pHs than in acidic pHs; these variations are also well reflected in partial apparent specific volume and partial apparent specific adiabatic compressibility. These findings are supported by the theoretical prediction from molecular dynamics simulations, which states that changes in the protonation states clearly affect the number of hydrogen bonds (HBs) and their orientations. By the quantitative analysis of protein-protein, protein-water, and protein-urea interactions, in acidic conditions, there is a decrease in total HBs: ∼307 HBs, ∼410 HBs, and ∼414 HBs were observed in acidic, neutral and alkaline conditions, respectively. As a result, OVA-water interactions have two distinct preferential solvations at extreme pHs: they are unfavorable in acidic environments and favorable in alkaline media.